The present invention relates generally to terminations for connectors and more particularly to connectors used in connections with signal cables, especially high-speed signal cables, and printed circuit boards.
Many electronic devices rely upon transmission lines to transmit signals between related devices or between peripheral devices and circuit boards of a computer. These transmission lines incorporate signal cables that are capable of high-speed data transmissions.
These signal cables may use what are known as one or more twisted pairs of wires that are twisted together along the length of the cable, with each such twisted pair being encircled by an associated grounding shield. These twisted pairs typically receive complimentary signal voltages, i.e., one wire of the pair may see a +1.0 volt signal, while the other wire of the pair may see a xe2x88x921.0 volt signal. Thus, these wires may be called xe2x80x9cdifferentialxe2x80x9d pairs, a term that refers to the different signals they carry. As signal cables are routed on a path to an electronic device, they may pass by or near other electronic devices that emit their own electric field. These devices have the potential to create electromagnetic interference to transmission lines such as the aforementioned signal cables. However, this twisted pair construction minimizes or diminishes any induced electrical fields and thereby eliminates electromagnetic interference.
In order to maintain electrical performance integrity from such a transmission line, or cable, to the circuitry of an associated electronic device, it is desirable to obtain a substantially constant impedance throughout the transmission line, from circuit to circuit or to avoid large discontinuities in the impedance of the transmission line. The difficulty of controlling the impedance of a connector at a connector mating face is well known because the impedance of a conventional connector typically changes through the connector and across the interface of the two mating connector components. Although it is relatively easy to maintain a desired impedance through an electrical transmission line, such as a cable, by maintaining a specific geometry or physical arrangement of the signal conductors and the grounding shield, an impedance change is usually encountered in the area where a cable is mated to a connector. It is therefore desirable to maintain a desired impedance throughout the connector and its connection to the cable.
The present invention is therefore directed to a termination structure for providing improved connections between cables and connectors that provides a high level of performance and which maintains the electrical characteristics of the cable in the termination area.
Accordingly, it is a general object of the present invention to provide an improved connector for high-speed data transmission connections in which the impedance discontinuity through the connector is minimized so as to better attempt to match the impedance of the transmission line.
Another object of the present invention is to provide an improved connector for effecting a high-performance connection between a circuit board and an opposing connector terminated to a transmission line, wherein the transmission line includes at least one pair of differential signal wires and an associated ground and the opposing connector includes at least two signal and one ground terminal, the connector having a pair of signal terminals disposed therein and a ground terminal associated therewith, the signal and ground terminals of the connector being arranged in a manner so as to reduce impedance discontinuities from occurring when the connector is mated to the opposing connector.
It is a further object of the present invention to provide such a connector wherein, by varying the size of the ground terminal and its location relative to its two associated signal wires, the impedance of the connector may be xe2x80x9ctunedxe2x80x9d to obtain a preselected impedance through the connector.
Yet another object of the present invention is to provide a connector for connecting cables, such as those of the IEEE 1394 type, to a circuit board of an electronic device, wherein the connector has a number of discrete, differential signal wires and associated grounds equal in number to those contained in the cables, the ground terminals of the connector being configured in size and location with respect to the signal terminals of the connector in order to minimize the drop in impedance through the connector.
It is yet a further object of the present invention to provide a connector for providing a connection between a circuit board and a connector associated with a signal cable, wherein the connector includes a pair of differential signal terminals and a ground terminal associated with the pair of signal terminals, the ground terminal being sized to control the impedance through the connector, the ground terminal of the connector being spaced apart from the pair of signal terminals in a contact area to establish a desired electrical relationship among the three terminals.
A still other object of the present invention is to provide a board connector for mating to a cable connector, the board connector having a housing, a ground terminal positioned within the connector housing and spaced apart from two associated signal terminals, the ground terminal having a body portion that is larger than corresponding body portions of the two signal terminal.
A yet further object of the present invention is to provide a board connector for use in connections with cables, the connector having a ground terminal and two signal terminals that are arranged in a triangular orientation within a mating contact portion of the board connector.
In order to obtain the aforementioned objects, one principal aspect of the invention that is exemplified by one embodiment thereof includes a first connector for a circuit board which has a housing that supports, for each twisted pair of wires in the mating signal cable, three conductive terminals in a unique pattern of a triplet, with two of the terminals carrying differential signals, and the remaining terminal being a ground terminal that serves as a ground plane or ground return to the differential pair of signal wires. A second connector for a cable is provided that mates with the first connector and this second connector also has a triplet pattern of conductive terminals that are terminated to signal and ground wires of the cable.
The arrangement of these three terminals within the first connector permits the impedance to be more effectively controlled throughout the first connector, from the points of engagement with the cable connector terminals to be points of attachment to the circuit board. In this manner, each such triplet includes a pair of signal terminals having contact portions that are aligned together in side-by-side order, and which are also spaced apart a predetermined distance from each other.
The ground terminal is spaced apart from the two signal terminals so that two rows of terminals are presented in the connector. The ground terminal has a contact portion that is spaced apart from like contact portions of the signal terminals, while the remainder of the ground terminal may extend between the signal terminals. In this extent, the ground terminal may extend in a common plane as the two signal terminals.
The width of the ground terminal and its spacing from the signal terminals may be chosen so that the three terminals may have desired electrical characteristics such as capacitance and the like, which affect the impedance of the connector. The width of the ground terminal will usually be increased in the mating area along the contact portions of the terminals, but it may also be increased in the transition area that occurs between the contact and termination areas of the terminals.
By this impedance regulating ground structure, a greater opportunity is provided to reduce the impedance discontinuity which occurs in a connector without altering the mating positions or the pitch of the differential signal terminals. Hence, this aspect of the present invention may be aptly characterized as providing a xe2x80x9ctunablexe2x80x9d terminal arrangement for each differential signal wire pair and associated ground wire arrangement found either in a cable or in other circuits.
In another principal aspect of the present invention, two or more such tunable triplets may be provided within the connector housing, but separated by an extent of dielectric material, such as the connector housing, an air gap, or both. In order to maximize the high speed performance of such a connector, the signal and ground terminals preferably all have similar, flat contacts that are cantilevered from their associated body portions so that the ground terminal contact portions may be selectively sized with respect to their associated signal terminals to facilitate the tuning of the terminals to obtain the optimum desired impedance in the connector system. When two such triple terminal sets are utilized in the connectors of the present invention, power terminals of the connector may be situated between the two triple terminal sets at a level equal to that of the ground terminals so as not to interfere with the signal terminals.
In still another principal aspect of the present invention, the connector has its ground and signal terminals arranged in a triangular orientation to maintain the predetermined spatial relationships that occur among these three terminals in the mating area of the board connector.